Brief introduction of HPM75 nonmagnetic steel; European metal HPM75 is a high-quality non-magnetic steel produced by Hitachi, Japan. It is a non-magnetic, high-hardness and corrosion-resistant plastic die steel produced by special smelting process, and it is a non-magnetic and high-strength austenitic non-magnetic die steel in HPM series steel. It can maintain stable austenite in various States and has very low magnetic permeability, so it is most suitable for mold products with high requirements for non-magnetism, corrosion resistance and wear resistance. Gas nitrocarburizing heat treatment can further improve the surface hardness and wear resistance, thus prolonging the service life of the die. The HPM75 non-magnetic steel is easy to work hardening, so it is suggested to work at low speed. Chemical composition of HPM75 nonmagnetic steel: C: 0.65-0.75% Silicon Si: 0.80% Mn: 14.50-16.00% Sulfur s: ≤ 0.030% P: ≤ 0.030% 2.00 to 2.50 percent of chromium Cr Mo Mo: 0.50-0.80% W: 0.50-0.80% 1.50 to 2.00 percent of vanadium V 2.70-3.30% of aluminum Al Characteristics of HPM75 nonmagnetic steel; 1. Pre-hardened steel with hardness of 42-45HRC without any heat treatment; 2. Pre-hardened steel most suitable for mirror polishing; 3. Excellent electrical discharge machining characteristics; (1) the treated surface is very good, which can replace etching processing; ⑵ When electrical discharge (EDM) machining is carried out, the surface hardness will not increase, which can simplify the subsequent machining process; 4. Uniform organization, which is most suitable for precision etching processing; 5. Good weldability, no hardening of surface chips, which can simplify the subsequent process; 6. Excellent toughness, excellent mechanical properties, and less worry about cracking. Scope of application of HPM75 non-magnetic steel: The features of HPM75, such as high hardness, wear resistance, corrosion resistance and non-magnetism, are comparable to many mold features such as stainless steel SUS304. HPM 75 is widely used for manufacturing non-magnetic mold fittings, non-magnetic bearings, magnetic plastics, magnetic field forming molds and structural components that require no magnetic induction in strong magnetic fields. HPM 75 is also suitable for manufacturing mirror polishing molds, precision corrugated processing molds, office automation equipment, auto parts, dust covers, TV filter plates, cosmetic boxes, etc. Supply status and metallographic structure of HPM75 nonmagnetic steel; Raw meal (black skin): 28-30 HRC; Clinker (black skin): 42-45HRC；; Hardness of surface treatment: ≥ 62 HRC; Metallographic structure: austenite. Heat treatment process of HPM75 nonmagnetic steel; The heat treatment process mainly includes: high temperature annealing process, solution softening process and aging hardening process; They are as follows: 1. High temperature annealing process The die material has high hardness and poor machinability. The purpose of annealing die at high temperature is to improve machinability, eliminate forging stress, facilitate die manufacturing and shorten machining cycle. Annealing process flow: annealing temperature is 870-890℃, heat preservation is 3-6h, the cooling rate from annealing temperature to 500℃ should be controlled, the cooling time should not be less than 6h, and the hardness is 28-30HRC. 2. Solution softening treatment process The solid solution process is to make the carbide of the material dissolve into the matrix, prepare the structure for the aging hardening treatment, and also improve the cutting performance, which is also called softening treatment in production; Equipment used: box type electric furnace (for preheating), high temperature salt bath furnace (for solid solution) or box type high temperature electric furnace; Technological process of solution softening treatment: when the balance is greater than 1.5-2mm, adopt high temperature box furnace for solution heating at 1150-1180℃, keep the temperature in salt bath furnace for 15-20min/mm, keep the temperature in box furnace for 30min/mm, and water-cool, the solution hardness of HPM75 is 20-22HRC, and the metallographic structure of the material is austenite+undissolved primary carbide. 3. Age hardening treatment process The purpose of aging hardening treatment after mold manufacturing and processing is to disperse and precipitate carbides dissolved in the matrix, so as to strengthen the matrix and improve hardness and wear resistance, which is also called hardening treatment in production; Adopt a box-type electric furnace, aging at 650-700℃ for 15-20h, water cooling or air cooling, and the hardness can reach 42-45HRC. Delivery specifications of HPM75 non-magnetic steel: Specification of European metal HPM75 round bar: φ 20 ~ 150 mm; European metal HPM75 sheet metal specification: 20 ~ 150 mm.
