Sintered metal parts and method for the manufacturing thereof

Inactive Publication Date: 2006-01-05
HOGANAS AB
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0007] It has unexpectedly been found that components having high fatigue strength can be obtained by shot peening of sintered components prepared from iron based powders distinguished by low levels of chromium and molybdenum.

Problems solved by technology

However, the sintered product has pores which are inevitably formed during the course of its fabrication.
These remaining pores of the sintered powder-metallurgical materials impair the mechanical properties of the materials, as compared with completely dense materials.
This is a result of the pores acting as stress concentrations and also because the pores reduce the effective volume under stress.
In this Distaloy®-powder the base-powder is alloyed with nickel, which is an expensive alloying element.
This high performing material is therefore rather costly and there is a need for less expensive materials, which have at least as good fatigue strength.
As indicated above there is an increasing demand for powders, which do not contain nickel, as nickel is expensive.
Other disadvantages with nickel containing powders are dusting problems which may occur during the processing of the powder, and which may cause allergic reactions also in minor amounts.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0015] Two pre-alloyed base-powders, Astaloy® CrL and Astaloy® CrM, and one diffusion-alloyed base powder, Distaloy® HP, are included in the study. Distaloy® HP is diffusion-alloyed with Ni and Cu and pre-alloyed with Mo. The three materials included in this study are shown in Table 1.

TABLE 1MaterialNi [%]Cu [%]Mo [%]Cr [%]Astaloy CrL0.21.5Astaloy CrM0.53.0Distaloy HP4.02.01.5

[0016] Detailed information on process parameters, density and carbon levels will be given below. In table 2 plane bending fatigue performance of un-notched specimen is shown for different alloys which are sintered 30 min in 90 / 10 N2 / H2 with cooling rate about 0.8 C / sec. Fatigue tests on un-notched specimens are performed using 5 mm ISO3928 samples with chamfered edges. The tests are made in four-point plane bending at load ratio F=−1. The staircase method is used with 13-18 samples in the staircase and 2 million cycles as run-out limit. Evaluation of the staircase (50% probability fatigue limit and standard ...

example 2

[0021] Influence of shot peening and the combination of heat treatment and shot peening has been investigated on Astaloy CrL 3 mm edge-notched specimens. The notch is included in the press tool and no machining is performed. The stress concentration factor in bending is obtained by FEM to Kt=1.38. Test frequency is 27-30 Hz.

[0022] The materials are sintered at 1280° C. for 30 min in H2. Cooling rate is 0.8° C. / s.

[0023] The shot peening is performed to obtain an Almen A intensity of 0.32 nm.

[0024] Estimated plane bending fatigue performance of as sintered and as-sintered plus shot peened samples is shown in table 5.

TABLE 5BendingCarbonDensitySecondaryFatigueIncreaseAs-SintAs-SintoperationLimitafter shotPowder[%][g / cm3]Shot peening[MPa]peeningAstaloy CrL0.707.30NO235notchedYES420+79%Astaloy CrL0.857.30NO340un-notchedYES450+32%

[0025] In table 6 an estimated plane bending fatigue performance of through hardened tempered and shot peened samples is shown. Through hardening is perform...

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Abstract

The invention relates to a method consisting of the steps of providing a pre-alloyed iron-based metal powder comprising at least 1.3-3.5% chromium, 0.15-0.7% molybdenum, manganese and unavoidable impurities, mixing said powder with 0.1-1.0% graphite, compacting the obtained mixture at a pressure of at least 600 MPa, sintering the compacted part in a single step at a temperature above 1100° C., shot-peening the part and after sintering optionally hardening the component. The invention also relates to a powder metallurgical part and use of a low chromium prealloyed powder for preparing notched sintered parts having a bending fatigue limit of at least 340 MPa at a sintered density of 7.15 g / cm3, preferably at least 400 MPa at a sintered density of 7.3 g / cm3.

Description

FIELD OF THE INVENTION [0001] The present invention refers to powder metallurgy and more specifically to pre-alloyed chromium powder metal parts with improved fatigue properties. BACKGROUND OF THE INVENTION [0002] In general, sintered products made by powder metallurgy are advantageous in cost over ingot steels obtained through forging and rolling steps and has wide utility as parts in e.g. motor vehicles. However, the sintered product has pores which are inevitably formed during the course of its fabrication. These remaining pores of the sintered powder-metallurgical materials impair the mechanical properties of the materials, as compared with completely dense materials. This is a result of the pores acting as stress concentrations and also because the pores reduce the effective volume under stress. Thus, strength, ductility, fatigue strength, macro-hardness etc. in iron-based powder-metallurgical materials decrease as the porosity increases. [0003] Despite their comparatively low ...

Claims

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Application Information

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IPC IPC(8): C22C33/02
CPCB22F2003/166B22F2003/248B22F2998/00C22C33/0264C22C33/0228
Inventor BERGMARK, ANDERSKANNO, KOKI
Owner HOGANAS AB
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