Hardness Testing in Cold-rolled Thin Steel Plates

Hardness tester in cold-rolled thin steel plate and steel strip hardness detection and application

Cold-rolled thin steel plate, referred to as cold-rolled steel plate, cold-rolled thin plate, cold-rolled plate, cold plate, etc. It also includes stainless steel plate, spring steel plate, hard steel sheet, galvanized plate, tin-plated plate, aluminum-plated plate, etc.

Cold-rolled thin steel strip, referred to as cold-rolled steel strip, cold-rolled strip steel, steel strip, strip steel, thin steel strip, cold-rolled coil, etc. It also includes stainless steel strip, galvanized steel strip, tin-plated steel strip, etc.

Cold-rolled thin steel plate and steel strip (hereinafter referred to as cold-rolled thin plate) are mainly used for stamping processing of parts, and the mechanical properties of cold-rolled thin plate are very important, which is directly related to the stamping performance of the plate. Cold-rolled sheets are graded according to different heat treatment states. Materials of different hardness are used for different processing methods.

National standard GB/T 13237-1991 "Superior carbon structural steel cold-rolled sheets and strips" roughly divides cold-rolled sheets into three grades: P grade for ordinary stamping, S grade for stamping, and Z grade for deep stamping.

China Metallurgical Standard YB/T 5059-1993 "Low Carbon Steel Cold-rolled Strips" divides thin steel sheets into five grades according to hardness, namely: TR (special grade), R (soft), BR (semi-soft), DY (low hard) and Y (cold hard). In fact, through a certain degree of cold rolling deformation and proper combination of heat treatment after cold rolling, the user's requirements for material mechanical properties can be met in a wide range.

Cold-rolled sheets can be divided into more grades according to the user's processing requirements. For example: Japanese Industrial Standard JIS G3141-1996 "Cold-rolled Carbon Steel Plates and Strips" is classified into three categories: general use (spcc), stamping use (spcd) and deep stamping use (spce), and is also subdivided into annealing, standard tempering, 1/8 hard, 1/4 hard, 1/2 hard, full hard and other levels.

The mechanical properties of cold-rolled thin plates can be tested by tensile tests or hardness tests. Since the hardness test equipment is simple, easy to master, the test efficiency is high, and there is a certain correspondence between metal hardness and strength, hardness testing is a more convenient method to determine the mechanical properties of materials.

The hardness test of cold-rolled thin plates can be used for quality control of the cold-rolled plate production process, and is more suitable for manufacturers of stamping products to re-examine the mechanical properties of raw materials.

The hardness tests specified in Japanese Industrial Standard JIS G3141-1996 are Rockwell hardness HRB and Vickers hardness HV. Vickers hardness test is used for cold-rolled thin plates without Rockwell hardness HRB, but it is not suitable for testing thin plate materials. Because when the plate thickness is less than 2mm, the HRB hardness test may cause the measured hardness value to be inaccurate due to the "anvil effect". For thin plate materials, the surface Rockwell hardness HRN or HRT can be tested and then converted to HRB or HV hardness.

At present, cold-rolled thin strip materials are developing in the direction of ultra-thinness, and cold-rolled thin strips with a thickness of 0.08mm have been rolled. Using the iqualitrol PHR-1S surface Rockwell hardness tester with a diamond point anvil, the hardness of cold-rolled thin strip materials as thin as 0.05mm can be tested.