The difference between Stainless steel hot rolled plate and cold rolled plate

/in /by

Stainless steel has excellent corrosion resistance, processing, biocompatibility and strong toughness within a wide range of temperatures, has been widely used in the petrochemical industry, atomic energy, light industry, textile, food, household appliances and other fields. Hot rolling and cold rolling are the necessary processes for stainless steel plate forming. The hot rolled plate is the raw material of cold-rolled plate, both of them will affect the microstructure of the stainless steel plate.

The hot rolling process of stainless steel is made from the slab (mainly continuous casting slab), which is heated and made from a roughing mill and finishing mill group. The hot steel from the last finishing mill is cooled by laminar flow to the specified temperature and is rolled into coils by the coiler. The steel after cooling has an oxide surface, with a black color, commonly known as “stainless steel black coil”. After annealing and pickling, the oxidized surface is removed, that is, “stainless steel white roll”. Some hot rolled stainless steel products can be used directly and some need to be processed into cold-rolled products before being used.

Stainless steel cold-rolled plate is generally the product of stainless steel hot-rolled plate with a thickness of 3.0-5.5mm after being rolled and processed by cold rolling equipment (single stand cold rolling/multi-strand cold rolling). Different processing methods and reprocessing after cold rolling can make the surface of stainless steel plate have different grades of surface finish, grain and color. There are 2D, 2B, No.3, No.4, No.4, HL, BA, TR, embossing and other surface grades in the surface processing of cold-rolled stainless steel plates. A variety of deeply processed surfaces such as electroplating, electropolishing, directional pattern, etching, shot peening, coloring, coating and its combination can be further implemented on the basis of cold rolling, in addition, the no.1 surface and pattern plate after hot rolling pickling are also included. what’s the difference between of hot rolled and cold rolled stainless steel plate?

 

Different surface qualities

Stainless steel cold-rolled plate has good surface quality, no oxide scale, a variety of surface treatments are available. Stainless steel hot rolled plate is generally No 1 treatment, with oxide skin, gray-white (pickling) or black-brown (not electroplated). The smoothness of the cold-rolled plate after electroplating is higher than that of a hot rolled plate.

 

Different prices

The toughness and surface quality of the stainless steel cold-rolled plate is higher than the hot-rolled plate, and the price is higher than the hot-rolled plate.

 

Different applications

Stainless steel cold-rolled sheet is widely used in various civil and industrial fields, including architectural decoration, products, home appliances, rail transit transportation, automobiles, elevators, containers, solar energy, precision electronics, etc. 2D, 2B, BA and grinding surface can be directly used for most products in architectural decoration, elevator, container and other industries. The cold-rolled sheet after forming or re-processing can be used in places with higher surface quality requirements, such as home appliances, rail transportation, automobiles, solar energy, precision electronics, etc.

What is Ferritic stainless steel used for?

/in /by

Ferrite stainless steel refers to the stainless steel with 11%~30%Cr and cubic crystal ferrite structure. Its high chromium content is the main element that affects its performance. The advantages of Ferritic stainless steel include low cost (without nickel), good magnetic conductivity, excellent stress corrosion resistance; Small working hardening tendency, easy to cold heading and cutting; High thermal conductivity (1.5 times that of Austenitic steel), low linear expansion coefficient (60% of Austenitic steel), but also obvious disadvantages such as poor plasticity and low strength in post-processing, easy welding cracking. Ferritic stainless steel is mainly used in oxidizing medium and nitride medium, suitable for heat exchange and heat circulation purposes, provides a wide range of applications.

 

Architecture and structure applications

Ferritic stainless steel is used as the roof and curtain wall of buildings because of its good resistance to atmospheric corrosion. High-chromium ferritic stainless steels used in coastal areas have been developed, and atmospheric corrosion-resistant stainless steels contain high levels of chromium and molybdenum and are supplemented with small amounts of niobium and titanium. The steel actually contains 22% chromium and 1.2% molybdenum. Sufficient chromium and molybdenum are necessary to improve the pitting resistance of stainless steel. The rusting area of type 304 and Type 316 austenitic stainless steel increased significantly with the increase of the number of periodic corrosion test cycles. On the contrary, the rust area of type 444 ferritic stainless steel increased slightly during the first 600 test cycles and was saturated after longer tests.

 

Automobile industry

Type 409 or 410L stainless steel is used as a vehicle exhaust emission control system material such as front pipe, center pipe and muffler due to its excellent intergranular corrosion resistance, formability and heat resistance. In recent years, the design temperature of vehicle exhaust has increased because of the catalytic conversion rate and reduction of harmful gases such as NOx, SOx and hydrocarbon (HC) emissions. However, the increased temperature of chromium carbide will produce deposits on the silencer, i.e., temperatures of 400 ~ 500℃will lead to grain boundary corrosion. Because the weld area is particularly sensitive to intercrystalline corrosion, it is necessary to improve the corrosion resistance of Ferritic stainless steel containing 12% Cr. Therefore, a new Ferritic stainless steel was developed by adding niobium to steel containing 12% Cr. It is well known that reducing carbon and nitrogen content in steel is quite effective in preventing intercrystalline corrosion. In this way, the intercrystalline corrosion resistance can be further improved by adding niobium and titanium to steel. 409L stainless steel is used as the material for the exhaust manifold of automobiles, and the exhaust temperature is designed to be about 800℃. 430J1L stainless steel is recommended when the exhaust temperature is approximately 900℃.

 

Home appliances and kitchenware

400 series ferrite stainless steel has been widely accepted in the field of household appliances and kitchenware because of its unique aesthetic properties, corrosion resistance to cleaners and disinfectants, low thermal expansion coefficient and magnetism (suitable for electromagnetic cookers). Ferritic stainless steel greatly reduces weight compared with carbon steel. Ferritic stainless steels do not contain nickel and are far more price stable than Austenitic steels, making it easier for manufacturers to manage costs, purchase and sell. The use of ferritic stainless steel is so wide, each use of the required ferrite stainless steel performance is different. Typical applications include dishwashers, electric kettles, washing machines, dustbins, kitchen drains, ovens, gas appliances, coffee makers, microwave ovens, gas stoves, cold storage, restaurant trolleys.

 

Ferritic stainless steel is also used in transportation and other industrial applications. Because it has so many advantages over carbon steel and Austenitic stainless steel, it’s excellent formability like bending, cutting and drilling making it has a wide applications. Because there are many ferritic stainless steel grades, in order to obtain good corrosion resistance, good strength and lower price, you need to choose the right grade to meet customer requirements.

Grades Chemical composition Characterize Applications
409L 11.3Cr-0.17Ti

Low C and N

 The added Ti making it has good high-temperature corrosion resistance and strength. Automobile exhaust pipes, heat exchangers, containers and other products without heat treatment after welding.
410L 13Cr

Low C

 Reduce the C based on 410, has good processing, welding deformation resistance, high-temperature oxidation resistance. Parts for mechanical construction, engine exhaust pipes, boiler combustor, burner.
430 16Cr Typical grades of ferrite steel, it has a low thermal expansion rate, excellent formability and oxidation resistance. Heat resistant appliances, burners, home appliances, tableware, kitchen sinks, external decorative materials, bolts, nuts, screen
430J1L 18-Cr0.5Cu-Nb

Low C&N

 Addition of Cu, Nb based on 430, good corrosion resistance, formability, weldability and high-temperature oxidation resistance. Building exterior decoration materials, auto parts, hot and cold water supply equipment.
436L 18Cr-1Mo-Ti、Nb、Zr

Low C&N

 Added Nb, Zr, excellent heat resistance and abrasion resistance, good processing and weldability. Washing machines, car exhausts, electronics, cooking POTS.

 

 

304 Stainless Steel VS 321 Stainless Steel

/in /by

Both grade 304 and 321 belong to the Austenitic 300 series stainless steel. They are similar in corrosion resistance, strength, hardness and welding performance, but 321 is mostly used in the heat resistance condition of 500-600 ℃. 321H stainless steel is the low-carbon version of 321, is the commonly used heat resistant steel, of which carbon content is slightly higher than 321 grades. 304 steel is an alternative to 321 stainless steel where intergranular corrosion resistance rather than high temperature strength is required.

In a way, grade 321 stainless steel is a new version based on grade 304 by adding Ti to improve the corrosion resistance of grain boundary and high temperature strength. As a stabilizing element, Ti element control the formation of chromium carbide, effectively, making 321 has a robust high-temperature strength, even much better than 304, 316L. A larger content of nickel makes 321 stainless steel has good abrasion resistance in different concentrations and temperatures of organic acids, especially in oxidizing media. 321 stainless steel has better Stress Rupture property and Creep Resistance Stress mechanical property than 304 stainless steel. Let me show exactly is the difference between them with the two tables below.

 

Chemical Composition of 304, 321, 321H

Grades C Si Mn Cr Ni S P N Ti
304 0.08 1.0 2.0 18.0～20.0 8.0～10.5 0.03 0.045 / /
321 0.08 1.0 2.0 17.0-19.0 9.0-12.0 0.03 0.045 0.1 5C-0.70
321H 0.04-0.1 1.0 2.0 17.0-19.0 9.0-12.0 0.03 0.045 0.1 0.16-0.7

 

Mechanical Property of 304 and 321

Grades Tensile strength, Mpa Yield strength, Mpa Elongation, % Hardness,HB
304 ≥520 205-210 ≥40≥40 HB187
321 ≥520 ≥205   HB187

 

As can be seen from the above table, 321 stainless steel contains titanium and more nickel (Ni) than 304, according to ASTM A182, the content of Ti should not be less than 5 times of carbon (C) content, but not more than 0.7%. Ti can prevent stainless steel sensitization and improve the high temperature service life, that is to say, grade 321 is more suitable for manufacturing wear-resistant acid containers, wear-resistant equipment and conveying pipes or other parts than 304 stainless steel in high-temperature environment.

304 and 321 stainless steel are both can be used for chemical, oil and gas, automotive fields. Grade 304  is general-purpose stainless steel and has the most extensive applications in the stainless steel family, such as tableware, cabinets, boilers, auto parts, medical appliances, building materials, chemicals, food industry, agriculture, shipping, oil transportation and so on. Grade 321 is used in chemical, coal and petroleum fields where required resistance to grain boundary corrosion and high temperature properties such as oil exhaust combustion pipes, engine exhaust pipes, boiler enclosures, heat exchangers, furnace components, diesel engine silencer components, boiler pressure vessels, chemical transport tanks, expansion joints, furnace pipes, etc