CS228287B1 - Method of heat treatment of cutting tools and forming tools - Google Patents

Abstract

The invention is a method of heat treatment of tools to reduce deformation after hardening. It is particularly suitable for tools such as cutters and dies for cutting and forming, plastic molds and other types of special tools, where the emphasis is on small dimensional changes during heat treatment. The essence of the invention is that the tool, before finalizing the shape and hardening, is heated to a temperature in the interval from + 30°C to the hardening temperature of the relevant oil for 30 minutes, cooled in oil to room temperature and tempered at a temperature of 55°C to 65°C for 1 hour, followed by cooling in air.

Description

The invention provides a method of heat treating a tool to reduce deformation after quenching. It is suitable for punch and die tools for cutting and molding plastics molds and other types of special tools, where the emphasis is on small dimensional changes in heat treatment ·

Removing distortions, which is commonly used in the hardening _of dooházá requires expensive operations (straightening, grinding), and which disproportionately increases the overall cost ·

Most of the deformations arise during heat treatment. Already when heated to an austenitizing temperature, the tools are deformed, especially if they contain asymmetrical residual stresses from previous machining, forming or due to rapid non-uniform heating. Normally, therefore, in the case of more national tools, one or more stages of preheating are selected after the roughing operations and before the final shape is finished, the stress relief is annealed and the gradual heating is ensured. However, the greatest proportion of deformations occurs during the actual hardening. This is due to the different specific volumes of the individual phases entering the heat treatment process (perlite, austenite, martensite), and the thermal and transformation stresses arise during cooling. Effective for reducing shape and dimensional deformations of steels with sufficient hardenability is quenching in environments with lower cooling efficiency (air compared to oil) or thermal quenching in salt baths. This technology is known and used in operations 1 when unacceptable deformations often occur.

The above mentioned drawbacks are eliminated by the method of heat treatment of the tools according to the invention, which consists in that the tool is heated to a temperature in the interval (Acj + 30 ° C) until the quenching temperature corresponding to ooeli for 30 min. oil to room temperature and tempered at 550 to 650 ° C for 1 h, followed by cooling in air.

228 287

The final hardening of such pre-treated tools is carried out according to the usual procedures recommended in the material sheets of the individual steels · Reduction of deformations in the application of the proposed process is caused by the reduction of volume and length increment during the second hardening and increased effect of thermal stresses on dimension reduction. This effect is supported by greater plasticity around the conversion temperatures A ^ and higher hot strength (especially in less alloyed steels). The beneficial effect is more pronounced in low- or medium-alloy steels without a high proportion of carbides (carbide-line tests) *, or with only a low content of dispersed NAD. Compared to conventional hardening without pre-heat treatment, the dimensional changes in the application of the proposed process are several times smaller for understeutectoid steels or only slightly overadutectoid, for limestone steels the deformation limitation is about 30%. For practical use of tools with small deformations after quenching, it is recommended to make the final shape with a minimum allowance for grinding after pre-refining, which replaces the stress relief annealing.

PROCEDURE IS SUITABLE FOR SHAPING AND FORMING TOOLS.

Frequently required low tool strengths, ie · 1000 to 1200 MPa, can be achieved by quenching from lower temperatures - approx. Ac ^ * JO ° C with different tempering temperatures · With such processing, both dimensional and shape changes are about half compared to conventional Hardening and high tempering to the same strength while significantly reducing power consumption ·

In the following examples the relative length changes of the spinning holes of the shear matrix 100x100x15 mm are given, the starting pitch of two circular holes of 8 mm being 80 mm.

• 100% sludge sludge length after quenching length in the annealed condition before quenching

Example 1 - Medium alloy tool steel

a) normal hardening according to material sheets 950 ° C / oil ............... * + 0,14%

b) quenching according to the proposed process 228 287 pre-treatment * conventional quenching (according to material data sheets):

840 ° C / oil + 580 ° C / l h / Air + 950 ° C / oil .........

..... / U »0.06%

Comparison of Examples 1a and 1b shows that by using the procedure, deformation was reduced more than 2X.

Example 2:

Medium alloy tool steel

(a) conventional quenching by sheet material

880®C / oil ........ Δ-Ϊ = + 0.14%

b) quenching according to the proposed process

1. pre-treatment + standard hardening (according to mat · list)

820 ° C / oil + 550 ° C / l h / air + 950 ° C / oil .........

....... / SX = + 0,07% (deformation reduced to 1/2)

2. pre-treatment + conventional hardening (according to mat · list)

880 ° C / oil + 550 ° C / lh / air + 900 ° C / oil .......

. ..ΛΧ = 0,03% (reduction of deformation to less than 1/4)

Example 3

Ledeburitic tool steel

a) normal hardening by material, sheet

950 ° C / oil ....... / i X «+ 0.18%

b) pre-treatment + conventional hardening (according to material data sheet)

840 ° C / oil + 600 ° C / lh / air * 950 ° C / oil .......

..... 4 X = + 0,12% excluded

Using pcstupnV, it reduced the deformation by about 1/3 ·

Claims (1)

object of the invention 228 287 Method for heat treatment of shear and forming tools from podeutectoid, nadeutectoid and ledeburitic tool steels, characterized in that, prior to the final shaping of the tool shape, it is heated to a temperature in the interval Ac ^ + 30 ° C at room temperature and tempered at 550 to 650 ° C for 1 hour followed by cooling in air.